Effect of SiO2 thicknesses in thermal-SiO2/PECVD-SiN stacks on surface passivation of n-type Cz silicon substrates

The influence of SiO₂ thicknesses in thermal-SiO₂/PECVD-SiN stacks on surface passivation of 2.5 Ωcm n-type Czochralski silicon substrates has been investigated. By annealing theses stacks in air we achieve surface recombination velocities (SRV) better (i.e. lower) than 2.6 cm/s for thin SiO₂ layers. We find a clear correlation between the thickness of the oxide layers and the annealing duration for obtaining optimum surface passivation. Furthermore, we also show that the absolute passivation quality of the SiO₂/SiN stacks correlates to the SiO₂ thickness. We find that the SRV increases with increasing oxide thickness. We also present data of the surface passivation of these SiO₂/SiN stacks after storage in the dark for several months. We find a slight degradation of the surface passivation for thicker oxides and no observable degradation for the 10 nm thick SiO₂ layer in our SiO₂/SiN stacks after 6 weeks of storage. Short annealing at 400°C in air restores the passivation quality and from then on remains unchanged for the measured storage time of 35 weeks.